The present invention relates to an apparatus for mixing a substance and a liquid diluent. The invention has particular application in the preparation of mixtures of a dry or liquid polyelectrolyte and water.
Polymers (used herein interchangeably with the term "polyelectrolyte") are commonly used in water treatment equipment in order to remove solids suspended in the water. Polymers carry an electrostatic charge which attracts particles suspended in water. Since virtually all solids carry a negative or positive charge, they are attracted to these polymers. Polymers have extremely large molecules with millions of charge sites that attract suspended particles. Synthetic polymers are available in dry and liquid form. Dry polymer is desirable for many applications because it has low weight, which saves on shipping expenses; can be easily stored and shipped in plastic lined sacks, which are relatively inexpensive as compared with disposable metal drums which must be used for liquid polymer, and has indefinite shelf life, whereas with liquid polymers the more dilute the mixture the shorter the shelf life. Furthermore, dry polymers have been approved as safe and effective in certain food grade and potable applications, whereas many liquid products have not received such approval. However, dry polymer must be mixed with water before it can be used. The dry polymer is hygroscopic and its suspension in water are thixotropic. In other words, the dry polymers do not readily mix with water. Many existing mixing systems are subject to agglomeration of dry polymer particles during the wetting/dispersing step.
In certain instances, a liquid polymer is the choice. Liquid polymers may be either of the solution type or the emulsion type. It would be desirable to provide a mixing apparatus which can be readily converted to process liquid polymer.